Arduino Power

Hi,

I have an AC/DC adapter with a 9.v / 500mA output. But when I try to measure the output on my Digital meter, it reads as 13.9v. and I'm wondering if I can use this adapter for my Arduino. Im just new here so please bear with me.

Thanks!

It's probably an unregulated type supply. Not sure which Arduino you have, but for an Uno (see the Summary section) the recommended maximum is 12V, however up to 20V should not damage the circuit. A problem may occur if too much current is drawn from the Arduino's supply, it could overheat its voltage regulator. Even this should not be fatal, they are made to turn themselves off if they get too hot, but obviously it's something to avoid.

If you're just going to run the Arduino and not a whole lot else (LEDs and such are fine) you should be OK. It would be interesting to measure the adapter's output voltage while it is powering the Arduino, I would expect it to drop some and that is a better measurement than an open circuit measurement. But good on you for checking it!

Here is some reading on the subject. I might prefer to get a regulated supply.
https://www.sparkfun.com/tutorials/103

Welcome to the forum!

Thanks for the reply. I am thinking to use this adapter on my UNO and Mega 2560. The other parts hooked into my arduino is the following:

*5v DC relay
*Voice Recognition Module -- Arduino

This adapter should not harm my arduino right?

Thanks again!

fynx:
Thanks for the reply. I am thinking to use this adapter on my UNO and Mega 2560. The other parts hooked into my arduino is the following:

*5v DC relay
*Voice Recognition Module -- Arduino

This adapter should not harm my arduino right?

Thanks again!

How much current do the relay and the VR module draw?

Not really sure how much current those modules draws from the board... :~ :~ :~ Any suggestions how to get it? :blush: :blush:

fynx:
Not really sure how much current those modules draws from the board... :~ :~ :~ Any suggestions how to get it? :blush: :blush:

If your meter is an ammeter not just a voltmeter, you measure current with it by breaking the circuit and putting the meter in series with the load.

So from a practical point, that might mean (say) unplugging the wire you have stuck in where ever you're getting the power from, sticking one probe of the meter into the now vacant place, and the other to the recently removed wire. (So the meter is in the circuit, not across the circuit like when you measure volts.)

fynx:
Not really sure how much current those modules draws from the board... :~ :~ :~ Any suggestions how to get it? :blush: :blush:

Measure it as Jimbo says, or read the spec sheets/data sheets from the manufacturer. Can you give us links to the relay and VR module?

I don't think I'd be too concerned if it's just a small relay, but it's always nice to know. Typical small 5V relays might draw 60 or 70mA, but bigger ones could be ten times that.

If the adapter continues to put out 14V, then the Arduino's voltage regulator has to drop 9V. 50mA for the Arduino, 70mA for the relay and just a SWAG for the VR board, say another 70mA, round up the total to 200mA. The voltage regulator has to dissipate 0.2A * 9V = 1.8W which means it'll get pretty warm. If a regulated 9V adapter were used, power dissipation would be less than half of that.

Take the above analysis as an example only, because I have no clue what current your gear actually requires.

Thanks I'll try that. here are the links for the modules:

Thanks for the help guys, you guys are awesome!

Well the VR module says 40mA. I don't see a spec for the relay. I might go ahead and hook it all up, and put a finger on the Arduino's voltage regulator. If it gets uncomfortable to leave your finger there, find another AC adapter.

On another note, the relay should almost certainly not be connected directly to the Arduino, but should be driven by a transistor. See the last page here for the proper way to connect it:
http://pgdev.pighixxx.com/ABC/SET/s1.pdf

Wow, thanks for pointing that out, I actually hooked the relay directly to my Arduino, better to take it off now before it permanently damage my Ardunio. :~:~:~

fynx:
Wow, thanks for pointing that out, I actually hooked the relay directly to my Arduino, better to take it off now before it permanently damage my Ardunio. :~:~:~

Hope it's not already damaged.

Looks like it's still working... Any sideeffects or indications that my board is damaged?

If there is damage, it may show up as some sort of problem with the pin it was connected to. Or it may not. Or something may happen at a later date. Worst case scenario, the MCU would need to be replaced. Easy on the Uno, not so easy on the Mega.

It seems to be working. Although when I measure the voltage coming out of the 5v pin, it only reads 4.89, is that normal?

fynx:
It seems to be working. Although when I measure the voltage coming out of the 5v pin, it only reads 4.89, is that normal?

That's only off by 2%, so yes, most likely that is normal. There are tolerances on all components like the voltage regulator. And also on voltmeters!